There are a number of different classes of surface flaws which may occur on smooth surfaces and which it is useful to detect and distinguish, especially in performing effective quality control. Such detection and differentiation of surface flaws is especially important, for example, with respect to the surfaces of nickel-plated aluminum substrates used in the manufacture of thin film magnetic media. One class of flaws is known as pits, which are local depressions with a diameter of from ten to several hundred microns, typically. The pits themselves may be smooth or contain breaks such as craters in their surfaces. A technique for detecting pits has been disclosed in a co-pending application for "Surface Pit Detection System and Method", Quackenbos et al., and is incorporated herein by reference. The second and third class of flaws, known as large defects and small defects, are closely related. Defects on the surface of rigid magnetic media may be the result of an impingement onto the surface or a tearing of material away from the surface. These types of defects can be very large scratches or gouges on the surface or very small (5 .mu.m and smaller) tears or pricks on the surface. The large surface defects, because of their size and scattering properties, are readily distinguishable through sophisticated data processing. The small surface defects (5 .mu.m and smaller) are not distinguishable since their scattering properties and physical size closely match that of adventitious surface contamination, which may be considered a fourth class of flaw.